How so? Who’s confused about what public domain means?
Laws.
You see, what various countries regard as Public Domain differs a lot. In Germany, for example, there's no way for someone to dedicate something to Public Domain at all. You simply can't waive your copyrights, period. Public Domain exists there, but it only consists of works which had their copyright expired or which have never had any copyrights assigned. If all you say is "I waive my copyright and dedicate this to Public Domain", then such declaration is simply invalid in Germany and may have no legal effect. This is why people use licenses such as CC0 to effectively emulate the effect of dedicating works to Public Domain even where there's no way provided by the law to do it.
There are more subtle effects involved when it comes to considering Public Domain status even between countries that happen to allow dedicating your works to it. It's very complicated. I still stand with all my comments about Public Domain being perfectly valid Open Source, but it has to be added that this assumes a CC0-like license (and patent grant if necessary) to make Public Domain dedication actually valid and non-ambiguous worldwide.
So, then public domain is only “open source” in theory but not in practice? You’re right, I’m wrong. OSI doesn’t recommend against public domain for the reasons I claimed, and I’m making mistakes in this discussion. Thanks for clarifying.
It can be Open Source in practice too, as long as you make sure that your Public Domain dedication is actually effective around the world. The best way to do that could be something like CC0, but CC0 itself is problematic because of its explicit no-patent-grant clause, so it's not recommended to use on software. Instead, licenses like 0BSD or MIT-0 are probably your best bet, practically emulating Public Domain and being officially recognized Open Source licenses.
The problem is that there's no such thing as "public domain" that is consistent in jurisdictions around the world. If you want to make something "public domain," the best way is to slap an OSI-approved license on it.
Comments
Laws.
You see, what various countries regard as Public Domain differs a lot. In Germany, for example, there's no way for someone to dedicate something to Public Domain at all. You simply can't waive your copyrights, period. Public Domain exists there, but it only consists of works which had their copyright expired or which have never had any copyrights assigned. If all you say is "I waive my copyright and dedicate this to Public Domain", then such declaration is simply invalid in Germany and may have no legal effect. This is why people use licenses such as CC0 to effectively emulate the effect of dedicating works to Public Domain even where there's no way provided by the law to do it.
There are more subtle effects involved when it comes to considering Public Domain status even between countries that happen to allow dedicating your works to it. It's very complicated. I still stand with all my comments about Public Domain being perfectly valid Open Source, but it has to be added that this assumes a CC0-like license (and patent grant if necessary) to make Public Domain dedication actually valid and non-ambiguous worldwide.
See also: https://opensource.org/faq#public-domain
So, then public domain is only “open source” in theory but not in practice? You’re right, I’m wrong. OSI doesn’t recommend against public domain for the reasons I claimed, and I’m making mistakes in this discussion. Thanks for clarifying.
It can be Open Source in practice too, as long as you make sure that your Public Domain dedication is actually effective around the world. The best way to do that could be something like CC0, but CC0 itself is problematic because of its explicit no-patent-grant clause, so it's not recommended to use on software. Instead, licenses like 0BSD or MIT-0 are probably your best bet, practically emulating Public Domain and being officially recognized Open Source licenses.
The problem is that there's no such thing as "public domain" that is consistent in jurisdictions around the world. If you want to make something "public domain," the best way is to slap an OSI-approved license on it.